The present invention relates to multilayer articles and their preparation. More particularly, it relates to multilayer articles comprising at least one polycarbonate layer, at least one polypropylene layer and at least one adhesive tielayer between the polycarbonate layer and the polypropylene layer.
The use of multilayer compositions for containers such as bottles, jars and the like, and packaging materials for storing food, beverages, and other perishable items has been known for quite some time. The advantage of using a multilayer structure is that the beneficial properties of two or more materials may be combined with the structural integrity of each material being essentially uncompromised. Usually the advantageous and positive properties of one material off-set or counter-balance the weaker properties of the second material. Thus, polycarbonate and polypropylene offer an attractive combination of properties which neither polymer can provide alone in a formed article. For example, polycarbonate resins exhibit advantageous properties of excellent impact strength, high heat resistance, gloss, and transparency. Polycarbonate resins also exhibit much better resistance to staining in food storage containers than does polypropylene. On the other hand, polypropylene offers better sound damping characteristics and is also less expensive than polycarbonate. Therefore, a multilayer article combining properties of a polycarbonate layer and a polypropylene layer is highly desirable.
To maintain structural integrity in formed, multilayer articles, polycarbonate and polypropylene layers must efficiently adhere to each other. However, highly polar polycarbonates have virtually no adhesion to non-polar polypropylene. A problem to be solved is to discover, a tie-layer which has adequate adhesion to both polycarbonate and polypropylene layers. The present inventors have tested many commercially available coextrusion tie-layers for such applications and found that they provided inadequate adhesion between polycarbonate and polypropylene layers. Also multilayer articles comprising polycarbonate and polypropylene layers joined by various tielayers were found to emit gas bubbles during microwave heating, adversely affecting both adhesion between the layers and also the aesthetic appearance of the article. It remains of interest, therefore, to develop a multilayer article comprising polycarbonate and polypropylene layers exhibiting efficient adhesion between the various layers.